import java.util.Scanner;
import java.util.*;

public class MC0408恢复回文 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        // code here
        String s = input.next();
        int count = 0;
        int left = 0, right = s.length() - 1;
        while (left < right) {
            if (s.charAt(left) != s.charAt(right)) {
                count++;
            }
            left++;
            right--;

        }
        System.out.println(count);
        input.close();
    }
}
